It's the first child for the Radio 1 presenter and partner Ben Cyzer.
The couple, who have been dating for 2 years, have named their new arrival Isaac but it is unknown how much he weighs or where the birth took place.
'Me and my lovely other half Ben are completely over the moon and feel incredibly blessed,' Sara told her listeners when she revealed she was expecting.
Sara's rep seemed surprised when asked for confirmation of the little boy's arrival.
'This is news to me,' she admitted.
Sara, 33, went on maternity leave last month and plans to return to work in September.
She's already mum to 3-year-old Lola, her daughter with estranged husband, DJ Jon Carter. She split from Jon in 2005 after 4 years of marriage.
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